In our application Ser. No. 11/566,306 being a c-i-p of Ser. No. 10/622,710, we describe microbore operations which create horizontal bores 2-6 m below ground for the introduction of pipes from 300-600 mm in diameter. These bring services such as sewerage, mains water, mains gas and the like to buildings where the runs are short but perhaps crowded such as suburban housing or industrial estates.
The operation is preceded by the selection of an on-ground direction between two sites. A pit is excavated at each site and a laser is used to indicate the direction below ground level. Inclination of the beam then follows to ensure appropriate fall. Meanwhile a concrete base is cast on the pit floor or timbers are laid and the pit wall which is to receive the bore is faced with concrete and a circular aperture is formed in the wall using a plug.
The drilling platform is lowered on to the base and a target on the shaft of the bore head and platform are aligned as a unit with the laser spot. The platform is secured in the pit using peripheral jacks and the ancillary services such as hydraulic power and mains water and vacuum operation are brought to the pit.
The specification proposes various improvements to the equipment. In our co-pending Australian Application No. 2006907085 we describe ancillary equipment with which the platform and bore head of this invention are intended to be used.
In our Australian Patent No. 2003262292 we describe a bore head in which a pair of rams disposed radially at 90° to each other. These are attached to the cylindrical wall of the bore head and are grouped at the leading end in order to provide the requisite steering movement, namely 15 mm either side of centre, while it would be preferable to place the target as close to the cutter as possible to give to the operator the truest possible picture of the drilling axis, the rams prevent this and the target therefore placed in front of the rams. While the operator had a good view of the laser spot on the target, the adjustment of the drilling axis would frequently result in oversteer.